Reactor system and process for the manufacture of ethylene oxide

ABSTRACT

A reactor system for the oxidation of ethylene to ethylene oxide. The reactor system includes a reactor tube that contains a packed bed of shaped support material that can include a catalytic component. The shaped support material has a hollow cylinder geometric configuration. The reactor system has specific combinations of reactor tube and catalyst system geometries.

[0001] The invention relates to reactor systems. Another aspect of the invention relates to the use of reactor systems in the manufacture of ethylene oxide.

[0002] Ethylene oxide is an important industrial chemical used as a feedstock for making such chemicals as ethylene glycol and detergents. One method for manufacturing ethylene oxide is by the catalyzed partial oxidation of ethylene with oxygen. In this method, a feedstream containing ethylene and oxygen is passed over a bed of catalyst contained within a reaction zone that is maintained at certain reaction conditions. Typically, the ethylene oxidation reactor is in the form of a plurality of parallel elongated tubes that are filled with supported catalyst particles to form a packed bed contained within the reactor tubes. The supports may be of any shape, such as, for example, spheres, pellets, rings and tablets. One particularly desirable support shape is a hollow cylinder.

[0003] One problem encountered with the use of a packed bed of hollow cylinder supported catalyst particles in an ethylene oxidation reaction zone is the difficulty in having a proper balance between the pressure drop that occurs across the catalyst bed during the operation of the ethylene oxide process and the catalyst bed packing density. Catalyst performance is generally improved with increased catalyst packing density in the ethylene oxidation reaction tubes; however, undesirable increases in pressure drop across the reactor generally accompany an increased catalyst packing density.

[0004] It is desirable in the manufacture of ethylene oxide by the partial oxidation of ethylene to utilize a reactor system with a packed catalyst bed having a high packing density but which the pressure drop across the packed catalyst bed is minimized.

[0005] It is, thus, an object of this invention to provide a reactor system suitable for use in the catalytic partial oxidation of ethylene oxide, which has a packed catalyst bed having a high packing density but still provides for a suitably low pressure drop during its operation.

[0006] Other aspects, objects, and the several advantages of the invention will become more apparent in light of the following disclosure.

[0007] According to one invention, a reactor system comprises a reactor tube that contains a shaped support material. The reactor tube has a length and diameter that define a reaction zone. Within the reaction zone is the shaped support material having a hollow cylinder geometric configuration. The hollow cylinder geometric configuration is defined by an inside diameter, an outside diameter and a length. A preferred embodiment of the reactor system includes the shaped support material having incorporated therein a catalytic component to thereby provide a supported catalyst system.

[0008] According to another invention, a process for manufacturing ethylene oxide includes introducing into a reactor system a feedstock comprising ethylene and oxygen and withdrawing from the reactor system a reaction product comprising ethylene oxide and ethylene. The reactor system comprises a reactor tube that contains a supported catalyst system. The reactor tube has a length and diameter that define a reaction zone. Within the reaction zone is the supported catalyst system that comprises a catalytic component supported on a shaped support material having a hollow cylinder geometric configuration. The hollow cylinder geometric configuration is defined by an inside diameter, an outside diameter and a length.

[0009]FIG. 1 depicts certain aspects of the inventive reactor system that includes a tube having a length that is packed with a bed comprising the shaped support material of a catalyst system;

[0010]FIG. 2 depicts the shaped support material of the catalyst system of the invention and which has a hollow cylinder geometric configuration and the physical dimensions that characterize the shaped support material;

[0011]FIG. 3 is a schematic representation of an ethylene oxide manufacturing process which includes certain novel aspects of the invention;

[0012]FIG. 4 presents data on the changes in pressure drop and tube packing density resulting from the use of various sizes of hollow cylinder support material with different length-to-diameter ratios in a 39 mm diameter reactor tube relative to the use of a standard 8 mm hollow cylinder support material;

[0013]FIG. 5 presents data on the changes in pressure drop and tube packing density resulting from the use of various sizes of hollow cylinder support material having a nominal length-to-diameter ratio of 1.0 and different bore diameters in a 39 mm diameter reactor tube relative to the use of a standard 8 mm hollow cylinder support; and

[0014]FIG. 6 presents data on the changes in pressure drop and tube packing density resulting from the use of various sizes of hollow cylinder support material with different length-to-diameter ratios in a 21 mm diameter reactor tube relative to the use of a standard 6 mm hollow cylinder support material.

[0015] One method of manufacturing ethylene oxide is by the catalyzed partial oxidation of ethylene with oxygen. The process is described in general in Kirk-Othmer, Encyclopedia of Chemical Technology, Volume 9, pages 432 to 471, John Wiley, London/New York 1980. Conventional ethylene oxidation reactor systems include a plurality of parallel elongated tubes that have inside diameters in the range of from about 20 mm to about 60 mm and lengths in the range of from about 3 m to about 15 m. Larger tubes for use in ethylene oxidation reactor system may also be possible. The tubes are typically suitable for use in a shell-and-tube type heat exchangers and are formed into a bundle for placement into the shell of the heat exchanger. The tubes are packed with any suitable ethylene oxidation catalyst that provides for the partial oxidation of ethylene with oxygen to ethylene oxide. The shell side of the heat exchanger provides for the passage of a heat transfer medium for the removal of the heat of reaction resulting from the oxidation of ethylene and for the control of the reaction temperature within the tubes containing the ethylene oxidation catalyst.

[0016] A feedstream comprising ethylene and oxygen is introduced into the tubes of the reactor system wherein the feedstream is contacted with the ethylene oxidation catalyst at temperature in the range of from about 50° C. to about 400° C. under a pressure in the range of from about 0.15 MPa to about 3 MPa.

[0017] The catalyst system used in the typical ethylene oxide manufacturing processes described above are supported catalyst systems that include a support or carrier material upon which is deposited or into which is impregnated a catalytic component and, if desired, a catalyst promoter component or components.

[0018] The inventive reactor system can be used in the oxidation of ethylene to ethylene oxide and includes a combination of a reactor tube and a shaped support material that is preferably a catalyst system. The unique geometry of this combination provides various unexpected process benefits.

[0019] The catalyst system component of the inventive reactor system can include a shaped support material that is impregnated with a catalytic component. Optionally, the shaped support material is also impregnated with one or more catalyst promoter components or catalyst copromoter components. The preferred catalytic component is silver. As for the promoter component, it can include, for example, rare earths, magnesium, rhenium, and alkali metals, such as lithium, sodium, potassium, rubidium and cesium. Among these, rhenium and the alkali metals, in particular, the higher alkali metals, such as, potassium, rubidium and cesium, are preferred. Most preferred among the higher alkali metals is cesium. Either the rhenium promoter may be used without an alkali metal promoter being present or an alkali metal promoter may be used without a rhenium promoter being present or a rhenium promoter and an alkali metal promoter can both be present in the catalyst system. In addition to the aforementioned promoters, a rhenium copromoter can be present in the catalyst system. Such copromoters can include sulfur, molybdenum, tungsten, and chromium. The promoter and copromoter compounds can be applied to the support material by any suitable method and in any form. Such forms include, for example, ions, salts, compounds and/or complexes. Their form may or may not, be changed to another form by the processing of the catalyst system.

[0020] The support material of the shaped support material and of the catalyst system can be any commercially available heat-resistant and porous material suitable for use as support material for the silver catalyst and promoter components of the catalyst system. These materials should be relatively inert under the reaction conditions prevailing in the oxidation of ethylene, and in the presence of the chemical compounds used. The support material can include carbon, carborundum, silicon carbide, silicon dioxide, aluminum oxide and mixtures of aluminum oxide and silicon dioxide. α-alumina is preferred, since it has a largely uniform pore diameter. It has a specific surface area of 0.1 to 10 m²/g, preferably 0.2 to 5 m²/g and more preferably from 0.3 to 3 m²/g (measured by the well-known B.E.T. method), a specific pore volume of from 0.1 to 1.5 cm³/g, preferably from 0.2 to 1.0 cm³/g and most preferably from 0.3 to 0.8 cm³/g (measured by the well-known mercury or water adsorption method), an apparent porosity of 20 to 120% by volume, preferably 40 to 80% by volume (measured by the well-known mercury or water adsorption method), a mean pore diameter of 0.3 to 15 μm, preferably 1 to 10 μm, and a percentage of pores having a diameter of 0.03 to 10 μm of at least 50% by weight.

[0021] The silver catalyst component and promoter components of the catalyst system are deposited on or impregnated into the support material of the catalyst system by any standard method known in the art. The catalyst system should have a concentration of silver or silver metal in the range of from about 2 weight percent to about 30 weight percent with the weight percent being based on the total weight of the catalyst system including the weight of the support material, the weight of the catalyst component, i.e., silver metal, and the weight of the promoter component or components. It is preferred for the silver component of the catalyst system to be present at a concentration in the range of from about 4 to about 22 weight percent and, most preferably, from 6 to 20 weight percent. The promoter or promoters can be present in the catalyst system at a concentration in the range of from about 0.003 weight percent to about 1.0 weight percent, preferably from about 0.005 to about 0.5 weight percent and, most preferably, from 0.01 to 0.2 weight percent.

[0022] The inventive reactor system includes a packed bed of the shaped support material or catalyst system having a greater tube packing density (TPD) than is found in conventional reactor systems. In many instances, it is desirable to increase the tube packing density because of the resulting benefits in catalyst performance. However, it is generally expected that to obtain higher tube packing densities, the pressure drop across the packed bed when in use will increase relative to standard reactor systems. The inventive reactor system, on the other hand, unexpectedly provides for less of an incremental increase in the pressure drop across the packed bed contained within the reactor tube of the reactor system than is expected, and, in many cases, a decrease in pressure drop across the packed bed, when compared to conventional systems, without a corresponding loss in tube packing density and, in many instances, with an increase in tube packing density.

[0023] It is preferred for the inventive reactor system to include a packed bed having a tube packing density at least as great as is found in conventional reactor systems, but preferably exceeding the tube packing densities seen in conventional systems, that when in use exhibit pressure drops that decrease with the aforementioned increase in tube packing density.

[0024] The relative geometries between the tube diameter and the shaped supports and/or catalyst systems is an important feature of the inventive reactor system, which includes the combination of a reactor tube packed with a bed of shaped supports which preferably include catalytic components to provide the catalyst systems. It is unexpected that larger supports, relative to the reactor tube, can be loaded as a bed within the reactor tube to obtain an increase in tube packing density either without observing a larger pressure drop across the packed bed when the reactor system is in use or with observing an incremental increase in pressure drop that is less than expected, particularly based on certain engineering correlations.

[0025] Larger supports and catalyst systems are particularly desired for use in the packed bed of the inventive reactor system with the packed bed having a greater tube packing density than is expected for the particular size of the support or catalyst system but which provides for no incremental pressure drop increase when in use and, preferably, an incremental decrease in pressure drop relative to that which is expected for reactor systems with the same tube packing density. Ant additional benefit can be an increase in the tube packing density.

[0026] In order to obtain the aforedescribed benefits, the inventive reactor system should include certain geometries. It has also been determined that these geometries are influenced by reactor tube diameters and, thus, the relative geometries of the reactor tube and the shaped supports are different for different tube diameters. For reactor tubes having an internal diameter of less than 28 mm, the ratio of the reactor tube internal diameter and support system outside diameter should be in the range of from about 1.5 to about 7, preferably, from about 2 to about 6 and, most preferably, from 2.5 to 5.0. For reactor tubes having an internal diameter exceeding 28 mm, the ratio of reactor tube internal diameter and catalyst support outside diameter should be in the range of from about 2 to about 10, preferably, from about 2.5 to about 7.5 and, most preferably, from 3 to 5.

[0027] The ratio of outside diameter-to-bore or inside diameter of the support of the catalyst system is another important feature of the inventive reactor system. For reactor tubes having an internal diameter of less than 28 mm, the ratio of outside diameter-to-bore or inside diameter of the support of the catalyst system can be in the range of from about 2.3 to about 1000, preferably, from about 2.6 to about 500 and, most preferably, from 2.9 to 200. For reactor tubes having an internal diameter exceeding 28 mm, the ratio of outside diameter-to-bore or inside diameter of the support of the catalyst system can be in the range of from about 2.7 to 1000, preferably, from about 3 to about 500 and, most preferably, from 3.3 to 250.

[0028] A further important feature of the inventive reactor system is for the support of the catalyst system of the packed bed of the inventive reactor system to have a length-to-outside diameter ratio in the range of from about 0.5 to about 2.0, preferably from about 0.8 to about 1.5 and, most preferably, from 0.9 to 1.1.

[0029] A summary of the desired ranges for the geometric dimensions of the inventive reactor system is presented in Tables 1 and 2. Table 1 presents the relative geometries of the shaped supports for reactor tubes having diameters that are less than 28 mm. Table 2 presents the relative geometries of the shaped supports for reactor tubes having diameters that exceed 28 mm. The larger reactor tubes can have tube diameters that range upwardly to about 60 mm or even larger, thus, the tube diameter of the larger reactor tubes of the inventive reactor system can be in the range of from 28 mm to 60 mm. TABLE 1 Inventive Reactor System Geometries For Reactor Tubes Having Tube Diameters of Less Than 28 mm Catalyst System Tube Diameter/ Length/Catalyst Catalyst Outside Catalyst System System Outside Diameter/Bore Outside Diameter Diameter Diameter Broad 1.5-7 0.5-2.0  2.3-1000 Intermediate   2-6 0.8-1.5 2.6-500 Narrow 2.5-5 0.9-1.1 2.9-200

[0030] TABLE 2 Inventive Reactor System Geometries For Reactor Tubes Having Tube Diameters of at Least 28 mm Catalyst System Tube Diameter/ Length/Catalyst Catalyst Outside Catalyst System System Outside Diameter/Bore Outside Diameter Diameter Diameter Broad  2-10 0.5-2.0  2.7-1000 Intermediate 2.5-7.5 0.8-1.5 3.0-500 Narrow 3-5 0.9-1.1 3.3-250

[0031] The reactor tube length can be any length that effectively provides for the proper contact times within the reaction zone between the feed reactants and the catalyst system to give a desired reaction product. Generally, as noted above, the reactor tube length will exceed 3 m and, preferably, it is in the range of from about 3 m to about 15 m. The full length of the reactor tube can be packed with the catalyst system or any portion of the length of the reactor tube can be packed with the catalyst system to thereby provide a packed bed of the catalyst system having a bed depth. Thus, the bed depth can exceed 3 m and, preferably, it is in the range of from about 3 meters to about 15 meters.

[0032] The packed bed, or catalyst bed, of the inventive reactor system should comprise a major portion of catalyst systems having the geometries as described herein. Thus, the catalyst bed of the reactor system will predominately comprise the catalyst system having the specifically defined geometries and, in particular, at least about 80 percent of the catalyst bed will comprise the specifically defined catalyst system, but, preferably, at least about 85 percent and, most preferably, at least 90 percent. When referring to the percent of the catalyst bed that comprises the catalyst system, it shall mean that the ratio of the total number of individual catalyst system particles having the particular dimensions described herein, divided by the total number of catalyst system particles contained in the catalyst bed, multiplied by 100.

[0033] The tube packing density of the catalyst system bed of the inventive reactor system can be an important feature of the invention; since, catalyst performance improvements can result from the increase in the tube packing density obtainable from using the unique geometries of the inventive reactor system. Generally, the tube packing density of the packed catalyst system bed depends somewhat upon the associated reactor tube inside diameter and on the properties, for example, density, of the particular support material used to form the shaped support.

[0034] For smaller reactor tube inside diameters the tube packing density of the packed bed can generally be less than the tube packing density of the packed bed of larger reactor tube inside diameters. Thus, for example, the tube packing density of the packed bed of an inventive reactor system having an inside reactor tube diameter of about 21 mm can be as low as, but exceeding, about 550 kg per cubic meters when the support material is predominantly alpha alumina. For reactor tubes having larger inside tube diameters as well as those having smaller diameters, it is desirable to have as great a tube packing density as is achievable and still realize the benefits of the invention. Such a tube packing density when the support material is predominantly alpha alumina can exceed about 650 kg per cubic meter or can be greater than about 700 kg per cubic meter and even greater than 850 kg per cubic meter. Preferably, the tube packing density is greater than about 900 kg per cubic meter and, most preferably, the tube packing density exceeds 920 kg per cubic meter. The tube packing density will generally be less than about 1200 kg per cubic meter and, more specifically, less than 1150 kg per cubic meter.

[0035] Reference is now made to FIG. 1 which depicts the inventive reactor system 10 comprising an elongated tube 12 and a packed bed 14 contained within elongated tube 12. Elongated tube 12 has a tube wall 16 with an inside tube surface 18 that defines a reaction zone, wherein is contained packed bed 14, and a reaction zone diameter 20. Elongated tube 12 has a tube length 22 and the packed bed 14 contained within the reaction zone has a bed depth 24. The elongated tube 12 further has an inlet tube end 26 into which a feedstock comprising ethylene and oxygen can be introduced and an outlet tube end 28 from which a reaction product comprising ethylene oxide and ethylene can be withdrawn. It is noted that the ethylene in the reaction product is the ethylene of the feedstock which passes through the reactor zone unconverted. Typical conversions of the ethylene exceed 10 mole percent, but, in some instances, the conversion may be less.

[0036] The packed bed 14 contained within the reaction zone is composed of a bed of supported catalyst system 30 as depicted in FIG. 2. The supported catalyst system 30 has a generally hollow cylinder geometric configuration with a nominal length 32, nominal outside diameter 34, and nominal inside or bore diameter 36.

[0037] It is the unique geometric combination of reaction zone diameter 20 and the geometric dimensions of the supported catalyst system 30 that provides for the unexpected reduction in pressure drop, when in use and relative to conventional systems, without a significant decrease in tube packing density. In many instances, and preferably, the tube packing density of the inventive reaction system is greater than that of conventional systems while still providing for a reduction in pressure drop when in use.

[0038] An essential geometric dimension of the catalyst system 30 is the ratio of nominal length 32 to nominal outside diameter 34. This dimension is described in detail above.

[0039] Another essential geometric dimension of the catalyst system 30 is the ratio of the nominal outside diameter 34 to nominal inside (bore diameter) diameter 36. This dimension is described in detail above.

[0040] The relative dimensions between the catalyst system 30 and elongated tube 12 are an important aspect of the invention; since, these dimensions determine the tube packing density and pressure drop characteristics associated with reactor system 10. This dimension is described in detail above.

[0041] Another way of defining the catalyst system is by reference to its nominal dimensions. For a standard 8 mm catalyst having a hollow cylinder geometric configuration, the outer diameter of the cylinder is nominally 8 mm but can be in the range from about 7.4 mm to about 8.6 mm. The length of the cylinder is nominally 8 mm but can be in the range from about 7.4 mm to about 8.6 mm. The bore diameter can be in the range of from about 0.5 mm to about 3.5 mm.

[0042] For a standard 9 mm catalyst having a hollow cylinder geometric configuration, the outer diameter of the cylinder is normally 9 mm but can be in the range of from about 8.4 mm to about 9.6 mm. The cylinder length while nominally 9 mm can be in the range of from about 8.4 mm to about 9.6 mm. The bore diameter of the standard 9 mm catalyst can be in the range of from about 0.5 mm to about 3.5 mm.

[0043] For a standard 10 mm catalyst having a hollow cylinder geometric configuration, the outer diameter of the cylinder is normally 10 mm but can be in the range of from about 9.4 mm to about 10.6 mm. The cylinder length while nominally 10 mm can be in the range of from about 9.4 mm to about 10.6 mm. The bore diameter of the standard 10 mm catalyst can be in the range of from about 0.5 mm to about 4.0 mm.

[0044] For a standard 11 mm catalyst having a hollow cylinder geometric configuration the outer diameter of the cylinder is normally 11 mm but can be in the range of from about 10.4 mm to about 11.6 mm. The cylinder length while nominally 11 mm can be in the range of from about 10.4 mm to about 11.6 mm. The bore diameter of the standard 11 mm catalyst can be in the range of from about 0.5 mm to about 3.5 mm.

[0045] Much of the variance in the catalyst system dimensions is due to the manner by which the hollow cylinder support material is manufactured. The manufacturing methods are known in the art of catalyst support manufacture and include such standard methods as extrusion methods and pill manufacturing methods.

[0046]FIG. 3 is a schematic representation showing generally an ethylene oxide manufacturing process 40 with a shell-and-tube heat exchanger 42 which is equipped with a plurality of reactor systems as depicted in FIG. 1. Typically the reactor system of FIG. 1 is grouped together with a plurality of other reactor systems into a tube bundle for insertion into the shell of a shell-and-tube heat exchanger.

[0047] A feedstock comprising ethylene and oxygen is charged via conduit 44 to the tube side of shell-and-tube heat exchanger 42 wherein it is contacted with the catalyst system contained therein. The heat of reaction is removed by use of a heat transfer fluid such as oil, kerosene or water which is charged to the shell side of shell-and-tube heat exchanger 42 by way of conduit 46 and the heat transfer fluid is removed from the shell of shell-and-tube heat exchanger 42 through conduit 48.

[0048] The reaction product comprising ethylene oxide, unreacted ethylene, unreacted oxygen and, optionally, other reaction products such as carbon dioxide and water, is withdrawn from the reactor system tubes of shell-and-tube heat exchanger 42 through conduit 50 and passes to separation system 52. Separation system 52 provides for the separation of ethylene oxide and ethylene and, if present, carbon dioxide and water. An extraction fluid such as water can be used to separate these components and is introduced to separation system 52 by way of conduit 54. The enriched extraction fluid containing ethylene oxide passes from separation system 52 through conduit 56 while unreacted ethylene and carbon dioxide, if present, passes from separation system 52 through conduit 58. Separated carbon dioxide passes from separation system 52 through conduit 61. A portion of the gas stream passing through conduit 58 can be removed as a purge stream through conduit 60. The remaining gas stream passes through conduit 62 to recycle compressor 64. A feedstream containing ethylene and oxygen passes through conduit 66 and is combined with the recycle ethylene that is passed through conduit 62 and the combined stream is passed to recycle compressor 64. Recycle compressor 64 discharges into conduit 44 whereby the discharge stream is charged to the inlet of the tube side of the shell-and-tube heat exchanger 42.

[0049] The following examples are intended to illustrate the advantages of the present invention and are not intended to unduly limit the scope of the invention.

EXAMPLE I

[0050] This Example I presents the testing procedure used to evaluate the pressure drop and tube packing density characteristics of the inventive reactor system relative to a standard reactor system.

[0051] Various hollow cylinder carriers having different sizes and geometries were tested in a commercial length reactor tube of either a 39 mm internal diameter or a 21 mm internal diameter. The reactor tubes were set up to measure differential pressure drop across the carrier bed. Tube packing density of the carrier bed was determined.

[0052] The particular carrier to be tested was loaded into the reactor tube using a standard funnel loading process. The carrier was weighed to determine its mass prior to being charged to the reactor tube. After the reactor tube was charged with the carrier, a 0.79 MPa (100 psig) air source was used to perform a 15 second dust blow down. The carrier bed height was measured.

[0053] The tube packing density was determined by using the mass of carrier loaded into the reactor tube, the measured height of the carrier bed, and the internal diameter of the reactor tube. The tube packing density has units of mass per volume and is defined by the following formula:

4m/πd²h

[0054] where:

[0055] m is the mass of the carrier loaded into the reactor tube,

[0056] d is the diameter of the reactor tube, and

[0057] h is the height of the carrier bed contained within the reactor tube.

[0058] After the reactor tube was loaded with the carrier, it was sealed and pressure tested at 1.342 MPa (180 psig). The reactor tube was equipped with an inlet and an outlet. Nitrogen gas was introduced into the inlet of the packed reactor tube at a pressure of about 1.136 MPa (150 psig). For each of about 11 different nitrogen gas flow rates a differential pressure drop (pressure drop) across the carrier bed of the reactor tube was determined by measuring the tube inlet pressure and the tube outlet pressure. The inlet and outlet temperatures of the nitrogen gas were also measured.

EXAMPLE II

[0059] This Example II presents a summary of the results from using the testing procedure described in Example I for hollow cylinder carriers of nominal sizes 5 mm, 6 mm, 7 mm, 8 mm and 9 mm having a nominal length-to-diameter (L/D) ratio of either 0.5 or 1.0 packed into a 39 mm reactor tube. Summary data for the percent changes in pressure drop across the carrier bed and the percent changes in tube packing density relative to the standard 8 mm carrier are presented in FIG. 4. As is shown, for carrier sizes smaller than 8 mm and for all carrier sizes having an L/D ratio of 0.5, the pressure drop across the carrier bed increases. The data presented in FIG. 4 does show, however, that in a 39 mm reactor tube, the larger 9 mm carrier that has an L/D ratio of 1.0 provides an improved pressure drop relative to a standard 8 mm carrier.

EXAMPLE III

[0060] This Example III presents the results from using the testing procedure described in Example I for hollow cylinder carriers of nominal sizes 9 mm, 10 mm, and 11 mm with a nominal L/D ratio of 1.0 and different bore diameters packed into a 39 mm reactor tube. Summary data for the percent changes in pressure drop across the carrier bed and the percent changes in tube packing density relative to the standard 8 mm carrier are presented in FIG. 5.

[0061] The data presented in FIG. 5 show the unexpected reduction in pressure drop that results from using the unique combination of reactor tube and carrier support geometry. For the 9 mm carrier having a ratio of bore diameter-to-outside diameter greater than 0.138 there is an improvement in pressure drop relative to a standard 8 mm carrier and for all the tested 10 mm and 11 mm carrier geometries there is an improvement in pressure drop relative to a standard 8 mm carrier.

[0062] As for the tube packing densities, an improvement is seen in the 9 mm carrier tube packing densities relative to a standard 8 mm carrier for geometries in which the ratio of bore diameter-to-outside diameter is less than about 0.38 and, for the 10 mm carrier, an improvement is seen for the geometries having a ratio of bore diameter to outside diameter of less than about 0.28. For the 11 mm carrier, improvements are seen in both the pressure drop and tube packing density for all the geometries tested.

EXAMPLE IV

[0063] This Example IV presents the results from using the testing procedure described in Example I for nominal carrier sizes 5 mm, 6 mm, 7 mm, 8 mm and 9 mm having a nominal length-to-diameter ratio of either 0.5 or 1.0 packed into a 21 mm reactor tube. Summary data for the percent changes in pressure drop across the carrier bed and the percent changes in tube packing density relative to the standard 6 mm carrier are presented in FIG. 6. As is shown, for the 8 mm and 9 mm carrier sizes an improvement in pressure drop is observed and for the 7 mm carrier having an L/D of 1.0 an improvement in pressure drop is observed.

[0064] While this invention has been described in terms of the presently preferred embodiment, reasonable variations and modifications are possible by those skilled in the art. Such variations and modifications are within the scope of the described invention and the appended claim. 

That which is claimed is:
 1. A reactor system comprising: an elongated tube having a tube length and a tube diameter of less than 28 mm which define a reaction zone; wherein contained within said reaction zone is a bed of shaped support material; wherein a major portion of said bed comprises said shaped support material; and wherein said shaped support material has a hollow cylinder geometric configuration defined by a ratio of nominal outside diameter-to-nominal inside diameter exceeding about 2.3, and a nominal length such that the ratio of said nominal length to said nominal outside diameter is greater than about 0.5.
 2. A reactor system as defined in claim 1 wherein said ratio of nominal outside diameter-to-nominal inside diameter exceeds about 2.6.
 3. A reactor system as defined in claim 2 wherein said ratio of nominal outside diameter-to-nominal inside diameter exceeds 2.9.
 4. A reactor system as defined in claim 3 wherein said tube length is an effective tube length exceeding 3 meters.
 5. A reactor system as defined in claim 4 wherein said major portion is at least half of said bed.
 6. A reactor system as defined in any one of claims 1 through 5 wherein said reactor system is further defined as having a ratio of said tube diameter-to-said nominal outside diameter in the range of from about 1.5 to about
 7. 7. A reactor system as defined in any one of claims 1 through 5 wherein said reactor system is further defined as having a ratio of said tube diameter-to-said nominal outside diameter in the range of from 2 to
 6. 8. A reactor system comprising: an elongated tube having a tube length and a tube diameter of exceeding 28 mm which define a reaction zone; wherein contained within said reaction zone is a bed of shaped support material; wherein a major portion of said bed comprises said shaped support material; and wherein said shaped support material has a hollow cylinder geometric configuration defined by a ratio of nominal outside diameter-to-nominal inside diameter exceeding about 2.7, and a nominal length such that the ratio of said nominal length to said nominal outside diameter is greater than about 0.5.
 9. A reactor system as defined in claim 8 wherein said ratio of nominal outside diameter-to-nominal inside diameter exceeds about 3.0.
 10. A reactor system as defined in claim 9 wherein said ratio of nominal outside diameter-to-nominal inside diameter exceeds 3.3.
 11. A reactor system as defined in claim 10 wherein said tube length is an effective tube length exceeding 3 meters.
 12. A reactor system as defined in claim 11 wherein said major portion is at least half of said bed.
 13. A reactor system as defined in any one of claims 8 through 12 wherein said reactor system is further defined as having a ratio of said tube diameter-to-said nominal outside diameter in the range of from about 2 to about
 10. 14. A reactor system as defined in any one of claims 8 through 12 wherein said reactor system is further defined as having a ratio of said tube diameter-to-said nominal outside diameter in the range of from 2.5 to 7.5.
 15. A reactor system comprising: an elongated tube having a tube length and a tube diameter of less than 28 mm which define a reaction zone; wherein contained within said reaction zone is a catalyst bed; wherein a major portion of said catalyst bed comprises a combination of a catalytic component and a shaped support material; and wherein said shaped support material has a hollow cylinder geometric configuration defined by a ratio of nominal outside diameter-to-nominal inside diameter exceeding about 2.3, and a nominal length such that the ratio of said nominal length to said nominal outside diameter is greater than about 0.5.
 16. A reactor system as defined in claim 15 wherein said ratio of nominal outside diameter-to-nominal inside diameter exceeds about 2.6.
 17. A reactor system as defined in claim 16 wherein said ratio of nominal outside diameter-to-nominal inside diameter exceeds 2.9.
 18. A reactor system as defined in claim 17 wherein said tube length is an effective tube length exceeding 3 meters.
 19. A reactor system as defined in claim 18 wherein said major portion is at least half of said bed.
 20. A reactor system as defined in any one of claims 15 through 19 wherein said reactor system is further defined as having a ratio of said tube diameter-to-said nominal outside diameter in the range of from about 1.5 to about
 7. 21. A reactor system as defined in any one of claims 15 through 19 wherein said reactor system is further defined as having a ratio of said tube diameter-to-said nominal outside diameter in the range of from 2 to
 6. 22. A reactor system comprising: an elongated tube having a tube length and a tube diameter of exceeding 28 mm which define a reaction zone; wherein contained within said reaction zone is a catalyst bed; wherein a major portion of said catalyst bed comprises a combination of a catalytic component and a shaped support material; and wherein said shaped support material has a hollow cylinder geometric configuration defined by a ratio of nominal outside diameter-to-nominal inside diameter exceeding about 2.7, and a nominal length such that the ratio of said nominal length to said nominal outside diameter is greater than about 0.5.
 23. A reactor system as defined in claim 22 wherein said ratio of nominal outside diameter-to-nominal inside diameter exceeds about 3.0.
 24. A reactor system as defined in claim 23 wherein said ratio of nominal outside diameter-to-nominal inside diameter exceeds 3.3.
 25. A reactor system as defined in claim 24 wherein said tube length is an effective tube length exceeding 3 meters.
 26. A reactor system as defined in claim 25 wherein said major portion is at least half of said bed.
 27. A reactor system as defined in any one of claims 22 through 26 wherein said reactor system is further defined as having a ratio of said tube diameter-to-said nominal outside diameter in the range of from about 2 to about
 10. 28. A reactor system as defined in any one of claims 22 through 26 wherein said reactor system is further defined as having a ratio of said tube diameter-to-said nominal outside diameter in the range of from 2.5 to 7.5.
 29. A reactor system; comprising: an elongated tube having a tube length, an inlet tube end, an outlet tube end, and an inside tube surface which defines a reaction zone and a reaction zone diameter (D_(RX)); wherein contained within said reaction zone is a shaped support material having a hollow cylinder geometric configuration having a nominal inside diameter (ID), a nominal outside diameter (OD), and a nominal length (L); wherein the ratio of said nominal length to said nominal outside diameter is at least about 0.5; wherein the ratio of said reaction zone diameter to said nominal outside diameter is less than about 10; and wherein the ratio of said nominal outside diameter to nominal inside diameter exceeds 2.3.
 30. A reactor system as defined in claim 29 wherein the ratio of said nominal outside diameter to nominal inside diameter exceeds 2.9.
 31. A reactor system as defined in claim 29 wherein the ratio of said nominal outside diameter to nominal inside diameter exceeds 3.0.
 32. A reactor system as defined in any one of claims 29 through 31 wherein the ratio of said reaction zone diameter to said nominal outside diameter is less than 7.5.
 33. A reactor system as defined in claim 32 wherein said shaped support material further includes a catalytic component thereby providing a supported catalyst system.
 34. A process for manufacturing ethylene oxide, said process comprises: providing a reactor system comprising an elongated tube having a tube length, an inlet tube end, an outlet tube end, and an inside tube surface which defines a reaction zone and a reaction zone diameter (D_(RX)); wherein contained within said reaction zone is a supported catalyst system, said supported catalyst system comprises a catalytic component supported by a shaped support material having a hollow cylinder geometric configuration having a nominal inside diameter (ID), a nominal outside diameter (OD), and a nominal length (L); wherein the ratio of said nominal length to said nominal outside diameter is at least about 0.5; wherein the ratio of said reaction zone diameter to said nominal outside diameter is less than about 5.5; wherein the ratio of said nominal outside diameter to nominal inside diameter exceeds 2.3; introducing into said inlet tube end a feedstock comprising ethylene and oxygen; and withdrawing from said outlet tube end a reaction product comprising ethylene oxide and ethylene.
 35. A process as recited in claim 34 wherein said reaction zone is maintained under suitable ethylene oxidative reaction conditions including a temperature in the range of from about 150° C. to about 400° C. and a pressure is in the range of from about 0.15 MPa to about 3 MPa.
 36. A process as recited in claim 35, wherein said shaped support material comprises predominantly alpha-alumina, and wherein said supported catalyst system is contained within a packed bed comprising a major portion of said supported catalyst system and having a tube packing density greater than about 550 kg per cubic meter.
 37. A process as recited in claim 36, wherein said reaction zone diameter exceeds about 20 mm.
 38. A process as recited in claim 36, wherein said tube length is 3 meters.
 39. A process as recited in claim 36, wherein said major portion is at least 80 percent of said packed bed.
 40. A process as recited in claim 36, wherein said ratio of said nominal length to said nominal outside is in the range of from about 0.8 to about 1.5, wherein said ratio of said reaction zone diameter to said nominal outside diameter is in the range of from about 2 to about 10; and wherein said ratio of said nominal outside diameter to said nominal inside diameter is in the range of from about 3 to about
 500. 41. A process as recited in claim 34, further comprising: recovering from said reaction product a recovered ethylene product comprising ethylene and a recovered ethylene oxide product comprising ethylene oxide.
 42. A process as recited in claim 41, further comprising: combining said recovered ethylene product with said feedstock prior to the introducing step. 